Valve Regulated Lead Acid Battery

Valve Regulated Lead Acid Battery

VRLA batteries are maintenance free, non-hazardous and non-spillable. These batteries use a regulated electrolyte with sulfuric acid suspended in either an absorbent glass mat or gel.

They operate on the oxygen recombination principle. During charging the positive plates react with hydrogen gas to produce water. This reaction is capped off by a simple, safe low pressure vent system should overcharging occur.


Unlike flooded lead acid batteries, VRLA batteries do not require regular addition of water. The electrolyte in these batteries is sealed within the battery cell and a safety pressure relief valve keeps the hydrogen gas produced during charging from building up to unsafe levels. These batteries also have a self-discharge rate that is low enough to keep them charged for long periods of time in medical equipment, such as hospital beds or operating room lights.

The term “VRLA” is a broad description of several types of lead acid batteries. It is used to describe batteries that have been made using either an absorbent glass mat (AGM) or a gel-like material. These batteries are also known as a sealed lead acid, sealed VR wet cell, or maintenance free battery.

These batteries use a recombination technology that allows the oxygen evolved at the positive plates during a charge to recombine with the hydrogen from the negative plates, creating water and preventing water loss. The battery’s safety pressure relief valve is only activated under severe overcharging conditions, which prevents the formation of dangerous gasses that can build up in a closed space.

The safety features of a VRLA battery are important to consider when installing and charging them in a home or commercial setting. These batteries should never be stored or charged in a tight container, and the battery should always be kept upright to avoid damage from vibration.


VRLA batteries have made significant inroads into the market as a power solution that is regarded as maintenance-free. This is primarily due to their hermetically sealed design.

This sealed construction prevents valve regulated lead acid battery the battery from leaking electrolyte during normal operation and also provides protection from internal damage caused by overcharge. They contain a safety venting system that will release and then reseal the battery if it is overcharged.

The venting system also allows for the battery to be charged without removing it from its mounting location. This makes them a good choice for UPS backup and other critical power applications where the battery is regularly used but not removed for long periods of time.

In addition, a VRLA battery is less likely to develop sulfation than traditional lead-acid batteries because the sulfate that forms on the lead plates is released and washed away during the charging process. It is important to note, however, that sulfation is still likely to occur even if the battery is regularly charged and discharged because it is not possible to chemically reverse this process once it occurs.

VRLA batteries are available in a wide range of sizes and designs. They are popular with residential and commercial backup and cycling applications such as sump pumps, fire and security systems, UPS battery backups and riding toys. They are also commonly found as starting batteries for automobiles.


A VRLA battery has a valve designed to prevent loss of water as the result of oxygen evolution and hydrogen gas evolution during charging. This prevents water loss that can lead to battery damage. The recombination of oxygen and hydrogen also prevents the formation of sulfate on the negative plates during discharging, which extends battery life. The absence of water loss and sulfation means that a VRLA battery does not require regular topping start-stop car battery up of the electrolyte, which reduces inspection and maintenance requirements. This is why these batteries are often referred to as “maintenance free.”

A battery’s performance can be affected by the type of electrolyte it uses, the design and manufacturing methods used in the battery cell, and the amount of electrolyte available within the cells. The absorptive glass mat (AGM) separator plays a critical role in a VRLA battery, as its properties and degree of saturation affect the rate at which gases transfer from one plate to another and the extent to which the recombination process takes place.

The AGM separator’s pore volume, acid absorbency, compression characteristics and gas-transfer properties also have an impact on the battery’s performance and service life. Although there are products on the market that claim to reverse sulfation, there is no peer-reviewed evidence that these techniques actually achieve this. Sulfation prevention remains the best course of action, by regularly fully recharging the battery.


Valve regulated lead acid batteries are often called “maintenance-free” but that doesn’t mean they don’t require maintenance. They just need maintenance in a different way than traditional flooded lead-acid batteries.

A key difference is the battery’s sealed design, which prevents the leakage of electrolytes. These hermetically sealed batteries are also position insensitive, which makes them more resistant to physical damage and shocks.

In addition, VRLA batteries do not require regular water top-ups, as is the case with flooded lead-acid batteries. They still need to be properly charged, however. To check battery capacity, you should use a voltmeter to measure the voltage of the battery at various points during the charging and discharging cycles. This will help you to understand the battery’s capabilities and avoid undercharging or overcharging, which significantly reduces the battery’s life.

The main reason lead acid batteries fail is because they become sulfated, and this is preventable by periodically putting the battery through a full recharge cycle. There are some products on the market that claim to reverse sulfation, but no independent studies have validated these claims.

To check the state of charge, disconnect all loads from the batteries and measure the voltage with a voltmeter. If the specific gravity readings are low, it’s time to add some water. Be sure to open the vent caps and carefully look inside the fill wells. It’s important that the electrolyte level is at least 1/8 inch below the bottom of the fill well. When adding water, only use distilled or demineralized water.

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